The individual fertility decision-making process--the decision whether or not to have another child--can be represented by a subjectively expected utility model incorporating the individual's utility for family size, utility for sex composition, and subjective probability of obtaining various sex compositions. The proposed research will (a) develop and improve measures of subjective probabilities and of the utilities for various family compositions, using computer-assisted rank order and pair comparison techniques, (b) determine the role of sex preferences (including preferences for a balanced sex composition) and of subjective probabilities by rigorously testing the proposed fertility decision-making model, (c) test the model for married couples of child-bearing age as well as for individuals, (d) investigate the way in which the preferences, utilities, and subjective probabilities of each spouse combine to form the couple's joint decision, and (e) find minimal measures for use in field settings. Because studies using parity-progression ratios (or transition probabilities) as a function of sex composition can be shown consistently to underestimate the impact of sex preference on fertility, a significant contribution of the proposed research will be the development of methods for better assessing this impact and the likely influence of sex predetermination techniques on fertility.